This application relates to optical communication networks.
Optical ring networks use one or more optical ring paths to optically link optical communication nodes. Each optical ring path may be formed by fibers or other optical links. Such optical ring networks can include a single fiber ring in some implementations and two separate fiber rings in other implementations. Either uni-directional or bi-directional optical communication traffic can be provided in optical ring networks. Optical ring networks can have various applications, including the access part of a network or the backbone of a network such as interconnecting central offices. Optical ring networks can be implemented to provide a protection switch as a “self-healing” mechanism to maintain continuous operation when an optical break occurs in the optical ring and can also allow for relative ease in adding and deleting nodes on the optical ring. In addition, WDM optical rings can provide direct peer-to-peer connections through wavelength add/drops without expensive regenerators. Furthermore, the cost of optical fiber deployment in a ring topology is generally much less than that in a mesh topology. Due to these and other features of optical ring networks, various optical ring networks have been widely deployed in metro and regional local area networks (LANs) for both data communication systems such as a token-ring LAN and Fiber Distributed Data Interface (FDDI) LAN) and telecom systems such as SONET/SDH optical networks.
Like other optical networks, an optical ring network may experience an unexpected break point in the signal traffic. For example, a fiber may break by, e.g., a fiber cut or a failure of an optical component in the ring such as an optical amplifier. The ring topology of optical ring networks allows a protection switching mechanism to be implemented for maintaining the operation of the optical ring network in presence of the break and for restoring the normal operation after the break is repaired.
The current carrier-grade quality of service requires the protection switching time to be less than 50 msec. Different protection switching mechanisms can be implemented in optical ring networks to meet this requirement. For example, SONET rings and resilient-packet-rings (RPRs) have been introduced to support efficient packet switching while meeting carrier-grade quality of service requirements mostly via SONET physical layer interface, including the protection switching time less than 50 msec. SONET or RPR rings currently deployed usually use optical-electrical-optical (O-E-O) regenerators to connect nodes to the ring and thus the O-E-O conversion is present at every span. This use of the O-E-O conversion can limit the overall capacity of the network to the capacity of the span with the smallest bandwidth in the ring. Therefore, when capacity upgrade is needed in SONET or RPR rings, every span of the ring network needs to be upgraded and such upgrade is referred to as fork lifting update and can be costly. Examples of the fork-lifting upgrade include: (a) a 2.5 G SONET ring grows to a 10 G SONET ring by upgrading every SONET ADMs in all nodes, and (b) a Gigabit Ethernet ring grows to a 10 Gigabit Ethernet ring by upgrading every switch/routers in all nodes.
Alternatively, WDM or DWDM optical ring networks can be implemented with all optical add/drop nodes on the ring without expensive O-E-O regenerator so that nodes are connected directly by multiple DWDM wavelengths to offer much higher capacity, reduced timing jitter, and improved signal latency and to allow for scalability, all at a reduced cost. Such an all-optical DWDM ring network relies on optical layer protection, whose recovery time is normally well within the currently required protection switching time of 50 ms for the carrier-grade quality of service.